1. Field of Invention
The present invention relates to a spark plug for use with an internal combustion engine, and more particularly, to the center electrode thereof having an improved construction.
2. Prior Art
The tip of the center electrode of a spark plug is directly exposed to a hot air-fuel mixture in the combustion chamber of an internal combustion engine. Therefore, the spark is required to have not only high chemical durability which is capable of withstanding service under hostile conditions but also great resistance to the wear that results from spark discharge. In order to meet these requirements, a noble metal tip is attached to the center electrode or the corresponding surface of the side electrode.
The spark plug with the noble metal firing tip has an improved spark resistance but the use of an expensive noble metal unavoidably increases the cost of the spark plug. Furthermore, spark plugs of this type are not adapted to high volume production since securely attaching the noble metal tip to the electrode axis involves special working and welding techniques.